6 Causes and Course of Organic Evolution 



garded as the element that starts energizing action, and that 

 passes on and distributes energy to the other three, so as to 

 cause these to hnk up in ever-increasing complexity. 



Of the metallic elements, potassium, calcium, magnesium, 

 and iron are most abundant in living tissues. They exist there 

 in various degrees of combining complexity. 



We may now briefly glance at the views generally held by 

 physicists and geologists of the present day, as to the evolution 

 of the earth's crust; the disposition of materials in it as gradual 

 cooling took place; the relation of land, water, and air to each 

 other as these became differentiated; also the environmental 

 relations which probably prevailed when conditions had be- 

 come favorable for the appearance of primitive organisms on it. 



In the gradual condensation and cooling of the earth from 

 an originally nebulous or gaseous and then incandescent planet, 

 it seems possible and even probable from the studies made by 

 Arrhenius (8) that the most abundant or the densest elements 

 such as platinum, gold, bismuth, and iron tended to gravitate 

 toward the center, to form there a gaseous core composed 

 very largely of iron, mixed in much smaller proportions ^^^th 

 other and rarer metals such as platinum and gold, but all in 

 a highly compressed though gaseous state. According to 

 some, as this metalUferous core continued to condense, and 

 to radiate off heat, it became a solid mass round which the 

 lighter metals, and some of the nonmetals — notably aluminium, 

 carbon, and silicon — collected either in pure state or in var^dng 

 chemical combinations between themselves and the heavier 

 metals within, or with the more gaseous bodies, such as oxygen 

 and hydrogen. 



But the metal iron, from its preponderating abundance in 

 the earth's core, and from the strains taking place between the 

 core and exterior, must have continually welled up, been ejected, 

 or exposed in large amount. Thus the rocks of archsean or 

 proterozoic age contain large deposits of iron, probably derived 

 in part from decomposition of igneous rocks, in part o%™g to 

 activity of primitive plant organisms (p. 16). Iron, therefore, 

 in all subsequent ages up to the present, has been the leading 



